Time temperature indicator

ABSTRACT

The present invention is generally in the field of measuring and indicating techniques and relates to a time-temperature indicator and methods of manufacturing and use thereof. More specifically, the time-temperature indicator comprises a time temperature indicator comprising at least one metal layer or metal containing layer and in direct contact to the metal layer or to the metal containing layer at least one doped polymer layer, wherein the dopant is an acid, a base or a salt or a photolatent acid or a photolatent base which dopant is added to the polymer, and/or at least one polymer layer wherein a polymer is functionalized with acidic or latent acidic or basic or latent basic groups; or a time temperature indicator comprising at least one polymer layer containing metal particles and a photolatent acid or a photolatent base, or at least one polymer layer containing metal particles wherein the polymer is functionalized with latent acidic or latent basic groups.

This invention is generally in the field of measuring and indicatingtechniques and relates to a time-temperature indicator and methods ofmanufacturing, dispensing and reading this indicator.

Time temperature indicators are devices that are characterized by atleast one changeable observable property that progresses in a rate thatis proportional to the temperature and time, and thus provide anindication of the full or partial time-temperature history of theirimmediate surroundings to which they are thermally coupled. Timetemperature indicators (TTIs) are simple and inexpensive devices,typically designed as labels. When attached to a perishable good, a TTI(appropriately designed and calibrated) monitors its time-temperaturehistory and provides a simple, usually visual, straightforward summaryof the exposure history of the product to time-temperature, therebyproviding indication of the product freshness condition. Consequently,TTIs are among the most promising shelf-life-report technologies.

The TTI concept was developed to ensure the safety and quality ofperishable goods, such as food and drug products, throughout theirentire lifespan, from manufacturing or packaging to the time they areconsumed by the end user. The safety and quality of many perishablegoods such as food, drugs, vaccines and blood, depend mainly onappropriate storage conditions during distribution and storage.Different factors such as gas composition, relative humidity andtemperature affect their real lifetime. The fact that changingconditions affect the effective shelf life of these kinds of goods isnot reflected by a “best before . . . ” type label that relies onappropriate storage conditions. Of all storage factors, temperatureabuse is the most frequently observed factor for pre-dateddeterioration, based on diverse physical, chemical, enzymatic ormicrobial processes. Therefore, the TTI technology can provide a simpletool for controlling the food and drug chain. The color and/or otherphysical properties of the TTI varies as a function of the time at arate which is temperature dependent, thus providing an active scale of“freshness” of the product to which it is attached, by comparing thecolor (or darkness) or any other varying visual property of the TTIlabel with a given comparative scale. Since the TTI indicators may bedesigned to provide a distinct “Yes” or “No” type of answer regardingthe time temperature factor, they may provide an important “clearcut”-answer and save further elaborate data inspection. This is idealfor HACCP (Hazard Analysis Critical Control Point), where the emphasisis on real time decision making and action.

Various TTIs are disclosed for example in the following patentpublications:

U.S. Pat. No. 6,435,128 discloses a time-temperature integratingindicator device that provides a visually observable indication of thecumulative thermal exposure of an object. The device includes asubstrate having a diffusely light-reflective porous matrix and abacking. The backing includes on its surface a viscoelastic indicatormaterial for contacting the substrate and a barrier material forsubstantially inhibiting the lateral and longitudinal flow ofviscoelastic indicator material between the substrate and the backing.

U.S. Pat. No. 6,042,264 discloses a time-temperature indicator device,designed as a label, for measuring the length of time to which a producthas been exposed to a temperature above a pre-determined temperature.The period of time of exposure is integrated with the temperature towhich the indicator is exposed. The label is a composite of a pluralityof layers adapted to be adhered at its underside to a product container.The label includes a printable surface layer, a longitudinal wickingstrip that is adhered underneath the surface layer substantially at theopposite extremities only of the wicking strip and a lower substratelayer forming an envelope with said surface layer. A heat-fusiblesubstance, which melts and flows above a pre-determined temperature, isapplied on the surface of the wicking strip contiguous to at least oneof the ends of the wicking member. When the heat-fusible substance isexposed to a temperature above the pre-determined temperature, theheat-fusible substance flows along the length of the wicking member. Thelabel has a printable surface layer and is sealed at its peripheral edgeto the peripheral edge of the substrate layer. These layers encapsulatethe wicking member and the heat-fusible substance. The surface layer isprovided with a sight window at an intermediate location over thewicking member through which the progress of flow on the wicking memberis observed.

WO 03/077227 discloses a time indicating label comprising a labelsubstrate having first and second surfaces, an acid-based indicatorcomposition, and an activator composition. One of the acid-basedindicator composition and the activator composition is on the firstsurface of the substrate, and both of these compositions when brought incontact remain adhered. The label may have a pressure sensitive adhesiveon the second surface of the label. The label provides an effectivemeans for determining the safety of frozen foods. The labels alsoprovide a means of providing security by providing name badges that aretime sensitive and may not be reused. The name badges provide a means tomonitor the length of a visitor's time and prevent reusing the namebadge.

WO 03/044521 discloses a sensor adapted to be remotely readable by RFtechniques for identification of the quality of a packaged foodstuff.The sensor either reacts with compounds generated in the atmosphere ofthe foodstuff package due to the microbiological decay of the foodstuff,for example hydrogen sulfide or other sulfide compounds, or the sensoris responsive to an increased oxygen content in the atmosphere of thepackage due to a leakage in the package. The sensor is based on a RFcircuit. Oxygen or the microbiologically generated gas affects theelectrical properties of the circuit material. For example, theresistor, the capacitor or the inductive coil of the circuit or at leasta fraction thereof are made of silver, iron, aluminium, a redox-typeindicator-dye, a conductive polymer, or copper. Due to the reaction ofthe aforementioned gases with these materials, the sensor resistance,conductivity, capacitance and/or inductance of the respective sensorelements changes depending on the amount of the disintegrating gas.

WO2006048412 (Freshpoint) describes a time temperature indicator devicecomprising at least 4 layers, a substrate layer, a salt layer and ametal layer and a polymer layer. The dry salt layer is evaporated atopthe substrate layer. The metal is in direct contact with the dry saltlayer. The metal layer covers the salt layer entirely to avoid that dueto humidity the salt starts to dissolve and affects the metal. Above themetal layer is a layer of a viscoelastic polymer. The viscoelasticpolymer has a solid to liquid transition when exposed to temperatureshigher than a certain threshold temperature. Being liquid theviscoelastic polymer diffuses through the metal and thus mixes the metallayer and the salt layer. Now the metal layer is etched and changes itsthickness and conductivity. The time temperature detection depends onthe viscosity of the polymer layer. For different threshold temperaturesdifferent polymers are required.

The problem underlying the present invention is to find a TTI which iseasily producible and in which the polymer layer can be tuned todifferent affecting agents, for example etching agents and to differentetching rates. In this configuration the TTI can be tailored todifferent time and temperature regimes by taking different affectingagents and polymers of different viscosity.

The problem is solved by providing a time temperature indicatorcomprising at least one metal layer or metal containing layer and indirect contact to the metal layer or to the metal containing layer atleast one doped polymer layer, wherein the dopant is an acid, a base ora salt or a photolatent acid or a photolatent base which dopant is addedto the polymer, and/or at least one polymer layer wherein a polymer isfunctionalized with acidic or latent acidic or basic or latent basicgroups; or

a time temperature indicator comprising at least one polymer layercontaining metal particles and a photolatent acid or a photolatent base,or at least one polymer layer containing metal particles wherein thepolymer is functionalized with latent acidic or latent basic groups.(Claim 1)

The doped polymer layer or the functionalized polymer layer in contactwith the metal is responsible for the time-temperature dependent changesin the optical, electrical, and/or electronic properties of the TTIand/or one or more of its components.

The doped polymer is, for example, etching, dissolving, fragmenting ordecomposing the metal thus causing a change in the optical and/orelectrical properties of the metal layer or the metal containing layer.

DEFINITIONS

Optical properties are, for example, absorption, transmission,reflectivity and the like.

Electrical and/or electronic properties are, for example, conductivity,resistance, capacitance, dielectric constant, inductance, resonancefrequency (RF) and the like.

The Polymer

The polymer is the carrier for the dopant and is a homopolymer, acopolymer, an adhesive or a viscoelastic liquid containing at least apolymer of the group consisting of polyethylene imine,polyethyleneglycoles, polysulfonates, polyacrylates, polymethacrylates,polyacrylic acid, polymethacrylic acid, polyvinyl alcohol,polyvinylchloride, polyvinylacetate, polyolefins, polyvinyl ethers,styrene/butadiene latexes, polyisobutylene, polyisoprene, polyurethane,polybutadiene, polychloroprene, butadiene acrylonitrile rubber, polyvinyl aryl phosphonic acid and/or esters, poly vinyl alkyl phosphonicacid and/or esters. The polymer layer may be composed of either one typeof a polymer or a mixture of polymers or even a mixture of polymers andoligomers or monomers.

Adhesives are natural adhesives or synthetic adhesives, for examplebased on elastomers, thermoplastic, and thermosetting adhesives.

Preferred are polyethylene imine, polyethyleneglycoles, polyacrylates,polymethacrylates polysulfonates, poly vinyl aryl phosphonic acid and/oresters, poly vinyl alkyl phosphonic acid and/or esters as well asmixtures thereof.

Especially preferred are polyacrylates and polymethacrylates andpolyethyleneimine, mostly polyacrylates and polymethacrylates as well asmixtures thereof.

Suitable additives serving as tackifiers for these polymers are rosin,rosin derivatives, hydrocarbon resins etc. Other additives such aswetting agents, plasticizers, fillers, preservatives and antifoamingagents are in some cases added.

A favoured viscoelastic liquid is prepared from copolymers of thepolyacrylate family. The monomer composition of these co-polymers is50%-90% of a main soft monomer (e.g. ethyl acrylate, n-butyl acrylate,2-ethylhexyl acrylate, iso-octyl acrylate etc.) which confers a low Tgto the material and thus high tack properties. The material is modifiedby 10%-40% of a secondary hard co-monomer (e.g. methylmethacrylate,t-butyl methacrylate, vinyl acetate, acrylic acid, etc.), which confershigher Tg to the material and thus higher peel adhesion. Functionalmonomers inducing crosslinking, improved wetting properties, andadhesion buildup are sometimes added (e.g. acrylic acid, methacrylicacid, itacronic acid, etc.). A preferred polymerization technique is oilin water (o/w) emulsion polymerization initiated by a radical initiator(e.g. ammonium persulfate, sodium persulfate, AIBN, etc.). Thepolymerization is performed in some cases in the presence of bufferingagents which improve the stability of final emulsion and allow a bettercompatibility of the components (e.g. ammonium hydroxide, sodiumhydroxide, disodium phosphate, etc.). The polymerization is performed inthe presence of non-ionic and/or ionic surfactants (e.g. sodium laurylsulphate, fatty alcohol ether sulphates, fatty alcohol polyglycol ether,polyvinyl alcohol, dodecylbenzene sulfonic acid etc.).

The Dopant

In one embodiment the dopant is a salt (claim 2).

The salt is preferably selected from the group consisting of watersoluble salts such as sodium chloride, potassium iodide, lithiumfluoride, potassium chloride, sodium iodide, lithium fluoride, sodiumcarbonate and the like. Mixtures of the salts are also possible.

In one embodiment the dopant is an acid. (Claim 3)

The acid is preferably selected from phosphoric acid, nitric acid,hydrochloric acid, sulphuric acid, polyphosphoric acid, pyrophosphoricacid, phosphonic acid, alkyl phosphonic acid (and derivatives), arylsulfonic acids and alkyl sulfonic acids (and derivatives) and the like.An example of an aryl sulfonic acid may be Dodecyl Benzene Sulfonic Acid(DBSA). Mixtures of the above acids are also possible.

In one embodiment the dopant is a base (claim 4).

The base is preferably selected from an alkali metal hydroxide, ammoniumhydroxide, tetra alkyl ammonium hydroxides, tetra alkyl ammoniumfluorides and the like. Mixtures thereof are also possible.

In one embodiment the dopant is a photolatent acid where the acid isreleased upon irradiation with light. (Claim 5)

Some photolatent acids are commercially available and are, for a nonlimiting example, selected, from the group ESACURE (Lamberti), IRGACURE(Ciba) e.g. IRGACURE® PAG103(2-methyl-α-[2-[[[(n-propyl)sulfonyl]oxy]imino]-3(2H)-thienylidene]-benzeneacetonitrile2(5H)-thienylidene]-benzeneacetonitrile), IRGACURE® PAG108(2-methyl-α-[2-[[[(n-octyl)sulfonyl]oxy]imino]-3(2H)-thienylidene]-benzeneacetonitrile),IRGACURE® PAG121(2-methyl-α-[2-[[[(4-methylphenyl)sulfonyl]oxy]imino]-3(2H)-thienylidene]-benzeneacetonitrile),IRGACURE® PAG203, Ethanone,1,1′-[1,3-propanediylbis(oxy-4,1-phenylene)]bis-[2,2,2-trifluoro-bis[O-(propylsulfonyl)oxime],UVI (DOW), CYRACURE (DOW),2-(-Methoxystyryl)-4,6-bis(trichloro-methyl)-1,3,5-triazine (Aldrich),sulfonates photoacid generators (Midori Kagaku).

In one embodiment the dopant is a photolatent base where the base isreleased upon irradiation with light. (Claim 6)

Some photolatent bases are commercially available and are, for a nonlimiting example, IRGACURE (Ciba) such as for example, IRGACURE® 369(2-Benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone asdescribed in EP 898202 or IRGACURE® 907(2-Methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone).

In yet other embodiments, the polymer is a functionalized polymer,functionalized with acidic or latent acidic or basic or latent basicgroups. These groups are chemically attached to the polymer, forming the“reactive polymer”. (claim 7)

A non limiting example for the photo production of phosphoric acid ispresented here as a non-restrictive example of the formation of an acidupon irradiation:

In some embodiments, it is preferable to use photosensitizers such asITX for improved spectral sensitivity and quantum yields for thephotoprocess.

The dopant is added to the polymer layer to the adhesive or to theviscolelastic liquid thus obtaining a “reactive polymer” which affectsthe metal due to its salt content or due to its acid or base content.The dopant is, for example, added in a concentration of 1-20%,preferably 1-10%. (claim 9)

The dopant is either dissolved in the polymer or blended into thepolymer. As the polymer layer may be a mixture of polymers, oligomers,monomers and additives, (as outlined above) and can also containsolvent, the dopant can be either dissolved or in any kind of aheterogeneous blend. For example the dopant and the polymer can form adispersion, an emulsion, a suspension and the like.

Functionalized Polymers

Polymers functionalized with acidic groups are, for example, polymershaving at least one —SO₃H, —PO₃H₂, COOH, substituent.

For example.

(Claim 8)

Polymers functionalized with basic groups, are, for example, polymershaving a basic nitrogen atom such as an amine group, a basic oxygen atomsuch as a hydroxyl group or an alkoxy group such as methoxy or ethoxy.

A polymer layer functionalized with a latent acidic or a latent basicgroup is a polymer generating a free acid or an acidic group or a freebase or a basic group upon irradiation with light.

Preferably the dopant is an acid or the polymer is functionalized withan acidic group.

It is also possible to use more than one doped polymer layer, (e.g. aplurality of pressure sensitive adhesive polymers (PSA's) havingdifferent concentrations of the dopant and/or different viscosities).The different layers may be side by side and/or on above the other sothat the reaction is not smooth but has accelerating or relentingeffects.

The Metal Layer/Metal Containing Layer

The time temperature indicator according to the invention comprises ametal layer or a metal containing layer, optionally incorporated into,or onto a substrate material such as, for example, polyolefin orpolyester films or paper.

Suitable metals for forming the metal layer are selected from aluminium,copper, silver, iron magnesium, titanium, tin, chromium, zinc, nickel,and alloys of these metals. (claim 10)

Preferred is aluminium. (claim 11)

The thickness of the metal layer is from 1 nm to 1 mm, and preferablyfrom 5 nm to 500 μm.

In one embodiment, the metal layer is a metal containing layerconsisting of inks containing metal pigment dispersions. (claim 12)

The wet film weight of the ink layer is from 1 to 50 g/m², preferablyfrom 2 to 30 g/m².

Suitable inks belong, for example, to the METASHEEN brand (Cibaspecialty chemicals) and METALSTAR, TOPSTAR, ULTRASTAR, ROTOSTAR,PRISMASTAR, PEARLSTAR and MFX brands (Eckart).

In one embodiment the metal layer are metal particles in a polymermatrix (claim 13).

In one preferred embodiment the doped polymer is polyethylene iminedoped with a water soluble salt selected from sodium chloride, potassiumiodide, lithium fluoride, potassium chloride, sodium iodide, lithiumfluoride, sodium carbonate.

In one preferred embodiment the time temperature indicator has analuminium metal (and/or metal containing) layer and a polyethylene iminelayer doped with potassium iodide.

In one preferred embodiment the doped polymer layer containspolyacrylate or a polymethacrylate and it is doped with an acid.

In another preferred embodiment the doped polymer layer containspolyacrylate or a polymethacrylate and it is doped with a base, with aphotolatent acid or with a photolatent base.

In another preferred embodiment, the doped polymer layer is an adhesivewhich is doped with an acid.

In another preferred embodiment the doped polymer layer is an adhesivedoped with a base, with a photolatent acid and with a photolatent base.

Some of the suitable adhesives are commercially available and areselected from, but not limited to, the group consisting of the followingmanufacturers BASF (ACRONAL A 240, ACRONAL V115, ACRONAL V215, ACRONALV220, ACRONAL V210, ACRONAL 80D, BUTOFAN LS103), TESA ( . . . ), VEROLIT(1740, 1763, 1764, 1860), DOW chemicals (UCAR, POLYOX), Celanese(Sensitac), POLYMER LATEX (Plextol) etc.

The lab-scale preparation of ACRONAL V115 doped with 5% H₃PO₄ (85% W/Win water) is given as a non limiting representative example for thepreparation of active glue layers. ACRONAL V115 (95 g) is stirred with apropeller-type stirrer (500-600 rpm) which creates a large vortex with amoderate shear. The acid (5 g) is added dropwise. The resulting mixtureis stirred for an additional 1-4 hours. The adhesive is applied on thecarrier as 40 microns thickness wet film and dried under an air flush at20° C.-70° C. The carrier with the dried adhesive is placed on a liner(release ribbon) for storage.

In another non limiting setup, the vinyl monomers corresponding to (a)and (b) and (c) below (typically 1%-20%) are oligomerized and/orpolymerized with (meth)acrylates monomers, thus leading to the formationof an inherently reactive acrylic adhesive. Tackifiers, wetting agents,plasticizers, fillers, preservatives and antifoaming agents are alsoadded in some cases.

Other dopants are in some cases added as described previously.

(c) for n=1 and R=Me is commercially available.

In another preferred embodiment the viscoelastic liquid (commercial ortailor made adhesive) is doped with a polymeric acid such aspoly(vinylbenzyl) phosphonic acid) (a) or poly((meth)acryloyloxyalkylphosphonic acid) (b)

In one embodiment, the acidic doped adhesive is compounded as a blend ofthe viscoelastic liquid with the acidic polymers at various ratios(typically 80%-99% and 1%-20%, respectively).

The metal layer or the metal containing layer and the doped polymerlayer may be superimposed, or they may lie as parallel stripes, dots orin any other geometry or geometric patterns. The thickness of the dopedpolymer layer is typically from 0.001 to 1.0 mm, and preferably from0.001 to 0.1 mm.

The Way to Activate the Time-Temperature Count

Each TTI system needs to be activated at a given time. There are twoways to initiate the activation.

In a one label system the metal layer or the metal containing layer isapplied onto a substrate and is in direct contact with the polymercontaining the photolatent dopant. Metal layer and polymer layer formone label. The activation is done by irritation with light. For exampleUV light is used.

A one label system is also a system consisting of one layer composed ofmetal particles in a polymer matrix, the polymer matrix contains aphotolatent dopant that is activated by light.

In a two label system, the metal layer or the metal containing layer isapplied onto a substrate and forms one label. The polymer layercontaining the dopant is applied onto a substrate and forms a separatelabel. The activation is made by contacting the labels.

In a one or two layer system where the activity is reduced considerably(practically to zero) by low temperatures, the activation starts bytaking the TTI for example out of a freezer.

Preparation Two Label System

In a further embodiment, the present invention also relates to a methodfor producing the time temperature indicator as described hereinbeforecomprising the steps of

a) doping a polymer by adding a salt, an acid or a base to the polymeror preparing a functionalized polymer thus obtaining a reactive polymer,b) applying the polymer of step a) on a substrate thus obtaining onelabel;c) applying a metal layer or a metal containing layer on a substratethus obtaining a second label.d) activating by applying the reactive polymer label of step b) onto themetal layer of step c) (claim 16)

Step c may be performed by vapour deposition or electrochemicaldeposition or in any other way. In case the metal containing layer is anink, the ink is printed onto the substrate.

One Label System

A method for producing the time temperature indicator as describedhereinbefore comprising the steps of

a) doping a polymer by adding a latent acid or a latent base to thepolymer or preparing a functionalized polymer having latent acidic orbasic groups thus obtaining a latent reactive polymer,b) activating the latent reactive polymer of step a by irradiation withlight thus obtaining a reactive polymer;c) applying the polymer of step a) on a metal layer or a metalcontaining layer on a substrate thus obtaining a label whereby placingone layer atop the other may be done either before activation or afteror at the same time; ord) adding a metal particles to the polymer layer that contains thelatent acid or base or to the functionalized polymer having latentacidic or basic groups and activating by irradiation with light. (claim17)

The substrate is preferably selected from the group consisting of paper,cardboard, paperboard, a plastic material (polypropylene, polyethylene,polyester) or metal.

The manufacturing process can be carried out using processingtechnologies suitable for packaging machines, preferably using gravureprinting, spray coating, inkjet, blade coating, offset, flexo,spincoating, silk screen printing, curtain coating, metering rod (Meyerrod) coating, slot die (extrusion) coating and/or lamination processes.The entire surface of the packaging material may also be coated by saidelectrical and/or optical temperature detector/indicator, and ifnecessary, self-adhesive labels may be manufactured therefrom forattaching on the package. Each layer may also be printed on itsrespective substrate followed by adhesion thereof with each other e. g.for producing self-adhesive labels. An adhesive layer may optionally beplaced between the layers.

The activation of the system (adhesion of two layers for the two labelssystem and light irradiation for the latent system) may be induced priorto the delivery onto the packaging. The activation may take place afterone or more layers are attached to the packaging.

The adhesion of the reactive layer to the metal layer may be carried outby using a device for dispensing labels. One dispenser attaches thelabel bearing the doped polymer layer to the surface of the metal layerwhile the second dispenser deposits the combined labels (doped polymerlayer+metal layer) atop the surface of the good to which the TTIindicator is to be attached. (claim 18)

A further embodiment is a method of activating and dispensing theclaimed TTI label comprising two label dispensers where one dispenserattaches the metal containing label atop the surface of the good towhich the TTI indicator is to be attached while the second dispenserdeposits the layer bearing the doped polymer layer to the surface of thesaid metal containing label. (claim 19)

A method of activating and dispensing a TTI label comprising a latentreactive layer by using a label dispenser that is equipped with a lightsource for activating the photolatent reactive layer.

The time temperature indicator may optionally be coated with aprotective layer.

Monitoring the Time Temperature History

The time temperature indication may be achieved electrically orelectronically by detecting a time temperature dependent change in theelectrical property or properties of the device and/or said metal layer.In the most simple case the electrical property is the resistance.(claim 14)

The time temperature indication may be achieved optically by detecting achange in an optical property (such as for example absorption,transmission, reflectivity) of the device and/or said metal layer itselfor optically measuring a prefabricated background of said metal layerwhich becomes accessible due to the time temperature dependentdissolution, disintegration, reaction, oxidation or any other processinflicted by the reaction of the metal containing layer and polymerlayer of said metal layer. For instance, a color change of the metallayer, which is preferably a colored electro-oxidized aluminum layer, isdetermined either visually by comparing to a reference sample, or usingan optical color reader, for example, by detecting a change of lightpower passing through the TTI. This change can also be observed in areflective mode.

A. change in electrical conductivity may be measured electrically usinga contact device by bringing two electrodes in contact to the timetemperature indicator, or by using RF techniques. Here the timetemperature indicator is incorporated as a part into a RF tag or RFID.The RFID containing an above described metal/polymer element will changeits characteristics upon time and temperature in a well defined fashion.

In one embodiment the metal layer is part of a capacitive device whichis characterized by at least two conductive layers i.e. at least twocapacitor plates with a viscoelastic polymer containing the dopant toplayer acting as the affecting layer and a second thindielectric/insulating layer between the conductive layers providing highcapacitance values. (claim 15)

Here the capacitance of the system changes as a function of the time andtemperature by either etching and/or dissolving

Instead of a capacitive geometry the metal layer may also be patternedto form the features of a RF tag (antenna, resistor or capacitor).(RF=radio frequency). which change properties (for instance Q factor)upon the time and temperature dependent etching of a metal layer,

FIGURES

The invention is further described by the figures which represent nonlimiting examples.

FIG. 1 is a resistor

It is a schematic illustration of a resistive TTI comprising one metallayer in contact with a doped polymer layer. The resistance is measuredwith two electrodes.

The following Table 1a shows the electrical conductivity/resistancerecorded in arbitrary units (a.u.) as a function of time at differenttemperatures. The doped polymer is Acronal V115 doped with 7% H₃PO₄ (85%in water). The metal is aluminium.

TABLE 1a Resistance Resistance Resistance Time (a.u.) at (a.u.) at(a.u.) at (min) 23° C. 14° C. 4° C. 0 5 5 5 200 0 4.9 5 600 0 0 5 1000 00 5 1750 0 0 4.8 2000 0 0 0

This example points out the drastic drop in electric potential(conductivity/resistance) of the TTI upon dissolution of the conductivealuminium layer.

The following Table 1 b shows also the temperature influence on thereaction rate. The metal layer is PVD aluminium Kurz skt20. (OD=0.67).The doped polymer is Acronal V115 doped with 5% H₃PO₄

TABLE 1b Resistance Resistance Resistance Resistance Time (a.u.) at(a.u.) at (a.u.) at (a.u.) at (h) 23° C. 15° C. 4° C. 2° C. 0 4.1 4.14.1 4.1 50 0 2 4.0 4.1 100 0 0 3.8 3.9 150 0 0 3.2 3.2 200 0 0 2.8 3.0250 0 0 1.8 2.0 300 0 0 0.5 0.6 350 0 0 0.1 0.2 400 0 0 0 0

The following Table 1c shows a direct correlation of the life time ofthe TTI to the thickness of the aluminium layer. The doped polymer isAcronal V115 doped with 4.25% H₃PO₄ Different PVD aluminium layers areused.

TABLE 1c Resistance (a.u.) Resistance (a.u.) Resistance (a.u.) Time Kurzskt 20 Kurz skt57 Dor film (h) OD = 0.7 OD = 1.7 OD = 2.2 0 4.0 4.2 4.548 0 4.0 4.5 96 0 3.6 4.4 144 0 2.9 4.3 192 0 2.5 4.2 240 0 1.7 4.1 2880 1.0 4.0 336 0 0.8 3.7 384 0 0.3 3.5

FIGS. 2 and 3 are capacitive devices.

FIG. 2 is a schematic illustration of a TTI structure according to oneembodiment of the invention, utilizing a capacitive device which ischaracterized by two conductive layers with a dielectric/insulatinglayer in between.

Layer 1 is a transparent conducting layer allowing the visual/opticalobservation of the etching process of the conducting layer 3, forexample an aluminum layer.

The doped polymer is the top layer of FIG. 2 (layer 4). The dopedpolymer layer is for example polyethylene imine (Mn=60,000 D, 50% inwater) doped with 10% KI

For creating high values of the capacitance (C) thedielectric/insulating layer 2 (Insulator) is in our example a thinpolymer layer (typically polyimide) with a layer thickness of typically10 to several 100 nanometers (layer two from the bottom). The aluminiumlayer is destroyed by etching. The system is both eye and machinereadable.

The following Table 2a shows the capacitance change of a TTI system asshown in FIG. 2. Due to the etching effect the capacitance decreases.This example demonstrates the effect of a sudden change in temperature(sample moved from 4° C. to 25° C.) on the electrical properties. Thedoped polymer layer is polyethylene imine (Mn=60,000 D, 50% in water)doped with 10% KI.

TABLE 2a Time (h) Capacity (pF) remark 0 3300 100 3500 200 3300 300 3300400 3250 450 0 Sample moved from 4° C. to 25°

The following Table 2b demonstrates the effect of the concentration ofthe inorganic salt on the rate of dissolution of the aluminium andsubsequent changes in the electric properties of the TTI. An increase inthe concentration of the electrolyte causes an enhancement of thereaction rate.

TABLE 2b Time Capacity (pF) Capacity (pF) (h) KJ 10% KJ 1% 0 2250 275010 250 2500 20 0 750 40 0 100 60 0 0

FIG. 3 is a schematic illustration of a TTI structure according toanother embodiment of the invention based on changing thedielectric/insulating layer between the capacitor plates. The secondlayer from the bottom is a dielectric/insulating layer, for example athin polymer layer (typically polyimide) as described at FIG. 2

This dielectric/insulating layer is very important to guarantee highinsulating values for the dielectric layer. Dielectric liquids rarelyhave very high insulation properties as needed for the device. There isan insulating/porous medium capable of letting a dielectric fluiddiffuse into the capacitor spacing. If one assumes that the liquid has ahigh dielectric constant (typically above 1.5 up to high values of 10and higher) the permeation of the liquid into the capacitor spacingincreases the capacitance of the device.

The insulating porous media is, for example, Whatman Nr 5 filter paperor a layer composed of granular insulator such as silica, alumina andalike. The viscoelastic liquid (the doped polymer layer) (PEI−Mn=60000D+KI) absorbs onto the porous media and diffuses through it, thuscausing changes in the capacitance of the system.

Table 3a shows the capacitance change of a TTI system as shown in FIG. 3

The viscoelastic liquid diffuses according to a time-temperaturecorrelation in the direction of the first capacitor (conductingsection). The capacity varies sharply when the viscoelastic liquidreaches the first conducting section. This example describes a setupwith one conducting section and subsequent single change in capacity. Asimilar experiment with multiple capacitor sections will bring aboutmultiple increasing steps in the capacity of the system.

TABLE 3a PEI on paper, room temperature Time (hr) Capacity (pF) 0 107 50112 100 115 120 127 130 135 140 145

Yet another example is the usage of the dielectric increase of thecapacitance C with time and temperature and combine this with the firstdescribed decrease of C with the etching of one (or both) of theconductive layers. Here one would create more complex time/temperatureprofiles. In this case the capacitance would first increase due todielectric effects and then decrease due to etching effects.

FIG. 4A-4D show optical systems.

FIG. 4A is a schematic illustration of a TTI structure according to theinvention that focuses on the optical properties of the device, lookingat the TTI through the doped polymer layer/metal (preferably Al)interface (doped polymer layer on top).

The metal containing layer of the device is placed atop the substratesuch as e.g. the package of a perishable good (1). The metal containinglayer is composed of a metal layer, preferably an aluminium layer (4), ametal carrier layer such as e.g. a PP film, PE film or paper (3) that isequipped with an adhesive on one side (2).

The reactive label is placed over the metal containing layer and iscomposed of a doped polymer layer (5) and a carrier layer (6). FIG. 4Ashows the device shortly before the reactive label is laminated to themetal containing part.

During storage the doped polymer layer (5) has to be protected tomaintain the polymer properties such as e.g. viscosity, humidity,reactivity and the like. An easily removable cover strip is applied tothe doped polymer layer. The cover strip may be a silicone film, PET andthe like. The carrier layer 6 can also act as protective layer.

The aluminum layer may be produced by one of any known techniques,including vapour deposition, electrodeposition, chemical deposition,electroless deposition and even deposited as printed ink (notnecessarily conductive). Alternatively, the aluminum layer may be partof the packaging material itself. This aluminum layer, as it isdescribed, is practically time-temperature stable.

The time temperature count of the TTI starts upon contacting thealuminium layer with the reactive label. The doped polymer reacts withthe aluminum layer (either chemically or physically) at a rate which istemperature dependent. Different signs may be placed behind the aluminumlayer in a way that it is exposed once the aluminum layer is consumed.

FIG. 4B is also a schematic illustration of a TTI structure according tothe invention that focuses on the optical properties of the device, inthis embodiment however looking at the TTI through the metal (preferablyAI) layer (metal top).

The upper label is the aluminum layer (4) and its carrier such as PP orPE (6). The time temperature count of the TTI starts upon contacting thealuminium layer with a reactive label consisting of a carrier layer suchas PP film, PE film or paper (3) that is equipped with an adhesive onone side (2) and a doped polymer (5) that reacts with the aluminumlayer. The carrier is placed atop a substrate, such as the package of aperishable good (1).

FIG. 4B shows the device shortly before the reactive label is laminatedto the metal containing part.

During storage the doped polymer layer (5) has to be protected asdescribed above under FIG. 4A

The major advantage here is that since aluminum is a highly reflectivelayer and the light does not penetrate it, it looks intact as long asthe reaction does not approach its surface that is exposed to theviewer. This offers a nice, close to step function response of the TTI.

FIG. 4C describes a side view of an embodiment for the TTI based on aprintable aluminium ink. An informative logo (2) and the background ofthe TTI (3) are printed on a substrate (1) such as PP, PET, PE, paper,cardboard etc. The printing process can be performed with all knownprinting and coating techniques such as rotogravure, flexography,inkjet, screen printing, reverse roll, Meyer rod, curtain coating, etc.The aluminium ink (4) is printed on top of the background. Theactivation begins upon contact with the doped polymer (5) and itscarrier (6) such as PP, PE or PET.

FIG. 4D describes a side view of another embodiment where the TTI isbased on a physically vapour deposited aluminium (PVD) layer. In thisembodiment, a substrate (1) such as PP,

PE, PET, or paper etc. is PVD metallized on one side, resulting in athin metal layer (4), preferably aluminium. The background of TTI (3) isprinted on the other side of the substrate. The informative logo (2) isprinted directly on top of the metal layer. The ink and printingtechniques for the impression of the logo are selected so that theprinted layer is non-reactive and non-permeable towards the dopedpolymer (5), acting as a protective layer for the PVD aluminium, thuspreserving a homogeneous background for the logo. Flexographic printingwith UV-curable inks is such a suitable printing process.

FIG. 4E shows a top view of the optical system. A label consisting of aninformative logo (2) in the centre of which a metal layer (preferablyaluminium) is applied (1). The aluminium layer is etched upon activation(contact with doped polymer) according to a time-temperaturecorrelation, eventually revealing the background (3).

FIG. 4F refers to a TTI setup where the metal layer consists ofaluminium inks, based on Metasheen® aluminium pigments from Ciba, whichwere etched with an ACRONAL V115 —H₃PO₄ (5.95%) system. The differentpigments are differentiated by their particle size and particle sizedistribution (particle size of the Metasheen inks: 91>71>41). The lighttransmission was recorded in arbitrary units (μWatt) as a function oftime and at a temperature of 40° C. The sample reached transparency atabout 500 μW. This example shows that the particle size of the metalpigments play a central role in the rate of dissolution of the metallayer.

FIG. 4G relates to a TTI setup wherein the metal layer consists of twoinks based on the Metasheen®-41 aluminium pigments from Ciba, which wereprocessed into inks by two different methods (varying essentially in thetemperature of processing). The aluminium inks were etched with anACRONAL V115 —H₃PO₄ (5.1%) system at 40° C. The light power was recordedas described above under FIG. 4F. This example illustrates the influenceof the ink processing technology on the time-temperature dependence ofthe metal etching process.

FIG. 4H shows further results obtained with 4.25% H₃PO₄ in Acronal V115at 40° C. The transparency is recorded as a function of the time and ofthe ink used.

FIG. 4I relates to a TTI setup where the metal layer consists of a PVD(physical vapor deposition) aluminium layer (0D=2.2). The etchingprocess was recorded at 0, 4, 7, 10, 15, 25, and 40° C. The dopedpolymer is an ACRONAL V115+4.25% H₃PO₄ etching system. A cleartime-temperature relationship is observed.

FIG. 4J relates to a TTI setup where the metal layer consists of a PVD(physical vapor deposition) aluminium layer (OD=2.2). The etchingprocess was recorded at 0, 4, 7, 10, 15, 25, and 40° C. The dopedpolymer is an ACRONAL V115++5.1% H₃PO₄ etching system.

A clear time-temperature relationship is observed.

1. A time temperature indicator comprising at least one metal layer or metal containing layer and in direct contact to the metal layer or to the metal containing layer at least one doped polymer layer, wherein the dopant is an acid, a base or a salt or a photolatent acid or a photolatent base which dopant is added to the polymer, and/or at least one polymer layer wherein the polymer is functionalized with acidic or latent acidic or basic or latent basic groups; or a time temperature indicator comprising at least one polymer layer containing metal particles and a photolatent acid or a photolatent base, or at least one polymer layer containing metal particles wherein the polymer is functionalized with latent acidic or latent basic groups.
 2. A time temperature indicator according to claim 1, wherein the dopant is a salt.
 3. A time temperature indicator according to claim 1, wherein the dopant is an acid.
 4. A time temperature indicator according to claim 1, wherein the dopant is a base.
 5. A time temperature indicator according to claim 1, wherein the dopant is a photolatent acid where the acid is released upon irradiation with light.
 6. A time temperature indicator according to claim 1, wherein the dopant is a photolatent base where the base is released upon irradiation with light.
 7. A time temperature indicator according to claim 1, wherein the dopant is a polymer which is functionalized with acidic or latent acidic or basic or latent basic groups.
 8. The time temperature indicator according to claim 7, wherein the functionalized polymer comprises monomers corresponding to (a), (b) or (c)


9. A time temperature indicator according to claim 1, wherein the dopant is added in a concentration of 1-20%.
 10. The time temperature indicator according to claim 1, wherein the metal is selected from aluminium, copper, silver, iron magnesium, tin, chromium, zinc, nickel, titanium and alloys of these metals.
 11. The time temperature indicator according to claim 10, wherein the metal layer is an aluminium layer.
 12. The time temperature indicator according to claim 1, wherein the metal layer is a metal containing layer and consists of inks based on metal pigment dispersions.
 13. The time temperature indicator according to claim 1, wherein the metal layer is a polymer matrix containing metal particles.
 14. The time temperature indicator according to claim 1, wherein the metal layer is part of a resistor device.
 15. The time temperature indicator according to claim 1, wherein the metal layer is part of a capacitive TT1 device which is characterized by at least two conductive layers with a dielectric/insulating layer in between.
 16. A method for producing the time temperature indicator as described in claim 1 comprising the steps of a) doping a polymer by adding a salt, an acid or a base to the polymer or preparing a functionalized polymer thus obtaining a reactive polymer, b) applying the polymer of step a) on a substrate thus obtaining one label; c) applying a metal layer or a metal containing layer on a substrate thus obtaining a second label d) activating by applying the reactive polymer label of step b) onto the metal layer of step c)
 17. A method for producing the time temperature indicator as described in claim 1 comprising the steps of a) doping a polymer by adding a latent acid or a latent base to the polymer or preparing a functionalized polymer having latent acidic or basic groups thus obtaining a latent reactive polymer, b) activating the latent reactive polymer of step a by irradiation with light thus obtaining a reactive polymer; c) applying the polymer of step a) on a metal layer or a metal containing layer on a substrate thus obtaining a label whereby placing one layer atop the other may be done either before activation or after or at the same time; or d) adding a metal particles to the polymer layer that contains the latent acid or base or to the functionalized polymer having latent acidic or basic groups and activating by irradiation with light.
 18. A method of activating and dispensing a TT1 label according to claim 1, comprising two label dispensers where one dispenser attaches the label bearing the doped polymer layer to the surface of the metal layer while the second dispenser deposits the combined labels atop the surface of the good to which the TT1 indicator is to be attached.
 19. A method of activating and dispensing a TT1 label according to claim 1, comprising two label dispensers where one dispenser attaches the metal containing label atop the surface of the good to which the TT1 indicator is to be attached while the second dispenser deposits the layer bearing the doped polymer layer to the surface of the said metal containing label.
 20. A time temperature indicator according to claim 9, wherein the dopant is added in a concentration of 1-10%. 